1. Field of the Invention
This invention relates to electrical switch devices and more particularly to a switch activating element comprised of a transducer member of a piezoelectric or electrostrictive type occasioned by the application of an electric field to said member.
2. Description of the Prior Art
Switches of the electromagnetic type have been used for many years. Such devices, have a relatively large mass and occupy considerable space, owing in part to the need for a magnetic field producing means. Switches embodying bimorph or bender transducers have also been made wherein one contact is at the end of a cantilever type linear element. The obvious disadvantage of this type of switch is that in order to obtain sufficient sensitivity, stiffness of the element must be sacrificed. This is because the sensitivity of the bender element is inversely proportional to the thickness, i.e. the distance between electrodes, of the bender element, whereas the stiffness of said element is directly proportional to the thickness. Accordingly, the movement of such an element is directly proportional to the thickness. The movement of such an element is in the thickness direction and because the stiffness of such element is limited, there is a tendency for such elements to sag under their own weight. Although the rigidity of such bender elements can be improved by increasing the thickness of the element, this would decrease the sensitivity and require unduly high voltages for operation. The only alternative is to sandwich several thin layers; however, such multiple layering is expensive and the bending problem becomes comparatively difficult.
In U.S. Pat. No. 3,405,289, entitled "Switch", dated Oct. 8, 1968, by E. Gikow, which patent is assigned to the assignee of the present invention, there is disclosed a switch wherein the transducer member is in the form of a split ring of piezoelectric material provided with a single pair of electrodes on opposite faces of the ring to which a unidirectional control voltage is applied. The fluctual movement of the split ring in response to the application of the control voltage causes the ends of the ring to move relative to one another, which by the connection of electrical switch contacts thereto in various configurations are actuated by the relative movement of the end faces of the ring which exist at the gap in the transducer ring.